Question: $ { \left[\begin{array}{rrr}{1} & {-1} & {3} \\ {3} & {1} & {1}\end{array}\right]+\left[\begin{array}{rrr}{-1} & {0} & {-2} \\ {0} & {1} & {-1}\end{array}\right] = {?} } $
Solution: To find the sum of two matrices, add the corresponding items between each matrix. ${\left[\begin{array}{rrr}{1}+{-1} & {-1}+{0} & {3}+{-2} \\ {3}+{0} & {1}+{1} & {1}+{-1}\end{array}\right]}$ Now, simplify: ${\left[\begin{array}{rrr}{0} & {-1} & {1} \\ {3} & {2} & {0}\end{array}\right]}$